1. Field of the Invention
The present invention relates to a method for fabricating a semiconductor device, and for example, a method for fabricating a semiconductor device, including a step of removing an opaque film formed on an alignment mark for alignment with an upper layer by ablation technology.
2. Related Art
As semiconductor devices have increasingly finer structures, higher precision of alignment technology with a lower layer is demanded in a lithography process among processes of manufacturing a semiconductor device. However, if a film formed in a resist lower layer reflects or absorbs a good portion of an alignment light, it is difficult to detect positional information from alignment marks. In a lithography process in which metallic wiring of, for example, aluminum (Al) is formed, there is a problem that the position of an alignment mark formed in a lower layer of an Al film cannot be directly detected because the Al film reflects or absorbs a good portion of the alignment light, that is, the Al film is opaque. Thus, an uneven form has conventionally been created at positions on an alignment mark on the surface of the Al film by providing a step height for the alignment mark itself in advance and subsequently forming the Al film. Then, by detecting an uneven form on the surface of the Al film, alignment has been performed. However, as the step height in the uneven form of an Al film created on an alignment mark becomes smaller with ever higher performance and precision of semiconductor devices, a problem of increasing alignment errors and decreasing lower yields has occurred.
Here, if detection sensitivity of an alignment mark should be enhanced, it is only necessary to remove an Al film on the alignment mark so that the alignment mark becomes visible. One method for this purpose is to add the lithography process for a region from which an Al film is to be removed, a dry etching process for the Al film, an asher process and the like. However, this method has a problem that the process becomes more complicated, resulting in increasing manufacturing costs, a longer manufacturing period, and increasing capital investment costs.
Thus, a method of selectively removing a film that is opaque with respect to an alignment light, such as an Al film, by ablation technology has been proposed as another method of removing an Al film on an alignment mark (see Published Unexamined Japanese Patent Application No. 2003-332215 (JP-A-2003-332215) and JP-A-2005-59064, for example). Ablation technology is one of processing technologies that use light such as a laser and enable microscopic patterns to be formed without using lithography technology, attracting attention in recent years as a processing technology of semiconductor devices. Ablation is a reaction in which a processed film melts or vaporizes if, when the processed film is irradiated with light, the intensity of irradiation reaches a certain threshold or more. Using this reaction, microscopic processing such as drilling and cutting can be performed. However, the wiring layer in a multilayer film tends to become thicker with ever higher performance, making processing by ablation more difficult without damaging areas around a processed film and a foundation thereof.
If, for example, an alignment mark is formed in a tungsten (W) embedded structure in a W plug layer and thereupon an Al film or a barrier metal film is formed as a wiring material, conventionally the Al film within a region around including the alignment mark and the barrier metal film in a lower layer of the Al film have all been removed using ablation technology. Here, if all films having a large reflectance like the Al film should be removed, it is necessary to increase laser energy of a laser to be a processing light or to apply a laser of a plurality of pulses. However, the threshold of ablation of silicon (Si) substrate and the W plug, whose reflectance is smaller, below the Al film is smaller than that of Al and it is difficult to remove the Al film only without damaging the W plug and substrate. As a result, the W plug to be a mark may also be removed together with the Al film. In such a situation, high-precision patterning cannot be performed because the alignment mark is removed. Further, a large amount of debris arises due to ablation, increasing debris in surrounding areas and causing a problem of dust.